1. Field of the Invention
The present invention is related to an inkjet head which ejects ink from nozzles, and more particularly to an inkjet head and an inkjet recording device which prevents clogging of the nozzles due to foreign materials in the ink, foreign materials attached in a fabrication process, and the like.
2. Description of the Related Art
Recently, in response to a request of higher quality for an image forming apparatus, technologies related to a higher resolution of an inkjet printer, a laser printer, and the like have been developed.
Especially, in a case of realizing the higher resolution for the inkjet printer, a higher density of the nozzles and finer liquid droplets are fundamental for the inkjet head. Thus, a smaller nozzle diameter for discharging the ink and a higher integration of the nozzles has been attempted.
Conventionally, in the inkjet head, clogging of the nozzles occurs due to the foreign materials included in the ink, aggregates caused by ink components, and the like. In a case of enhancing fining of the nozzle diameter as described above, an allowable size of the foreign material is reduced. Thus, there is a problem in which clogging occurrences of the nozzles are increased if the fining of the nozzle diameters is performed.
There are foreign materials causing clogging of the nozzles, other than materials originated in the ink itself, adhere to an ink passage in a fabrication process of the inkjet head. In the fabrication process of the inkjet head, each of parts is cleaned, and then is built under a clean environment (a clean booth, a clean room, and the like) which is highly maintained. Accordingly, it is not possible to completely prevent the foreign materials from adhering to the nozzles.
It may be possible to reduce the foreign materials and aggregates included in the ink by improving the ink parts and providing a filter. However, it is difficult to prevent clogging caused by the foreign materials adhering to a vicinity of the nozzles in the fabrication process.
Thus, it may be considered to form the filter for eliminating the foreign materials at the nearest location possible to the nozzles in a fabrication process of the parts, and to prevent an occurrence of clogging caused by the foreign materials adhering to the nozzles in a subsequent fabrication process.
However, in a case of forming the filter in the fabrication process of the parts for manufacturing the inkjet head, fabrication costs may increase.
For example, the nozzle diameter of a recent inkjet head for discharging droplets of a few pico liters is 10 μm to 20 μm. Thus, a high-precision process may be required to make an opening diameter of the filter for eliminating the foreign materials less than or equal to 10 μm. Also, a filter having a single thin layer is required to be formed at the parts. Thus, a micro fabrication is carried out to form an opening diameter of approximately 10 μm.
As above-described methods for the micro fabrication of the filter, an etching method using a photo-lithography, electroforming method, and the like are known. In any case, it is difficult to suppress an increase of the fabrication costs.
Moreover, due to the fining of the nozzle diameter and the higher density of the nozzles, an engineering development for fining an actuator or the like, which pressurizes a liquid chamber leading to the nozzles, has been advanced. Specifically, a Micro Electro Mechanical Systems (MEMS) technology using a semiconductor process technology has been deployed for the inkjet head. By using the MEMS technology, it is possible to form a diaphragm, a liquid chamber, an ink passage, an actuator, an electrode, and the like on a silicon wafer. It is also possible to micronize the nozzles, and the liquid chamber, and the like.
However, materials, which can be used as structural components such as the diaphragm, the filter, and the like in the MEMS technology, may be limited to materials made from a Chemical Vapor Deposition (CVD) such as Si3N4, SiO2, p-Si, and the like. For metal and alloy materials, a sputtering method, a vapor-deposition method, and the like are used as a film forming method. Accordingly, it is difficult to form compact films to be the structural components.
Alternatively, a photosensitive resin material such as a dry film resist, and the like, may be used as the structural components. It is required to make the film thicker in order to ensure stiffness of the film. As a result, a resolution is decreased. Moreover, it is difficult to form electrodes and the like on a resin material in terms of moisture resistance, surface properties, and the like. This method has limited application.
Accordingly, as a material used to form the compact filter by using the MEMS technology, an inorganic material such as silicon nitride may be used. However, the inorganic material is stiff, and has a sufficient internal stress. Thus, the inorganic material includes risks of deformation and damage due to an occurrence of cracks or the like.
In order to solve the above described problems, for example, Japanese Laid-open Patent Application No. 2008-18662 discloses a technology related to a liquid droplet jet apparatus which includes a channel unit which includes a liquid passage including a nozzle for discharging a droplet, an energy applying unit which applies energy to liquid in the liquid passage to discharge the liquid, and a laminated body which is formed by layering multiple plates and includes a filter for eliminating the foreign materials in the liquid supplied to the liquid passage.
In the liquid droplet jet apparatus according to Japanese Laid-open Patent Application No. 2008-18662, multiple through-holes passing through to the liquid passage are formed for each of the multiple plates, and the multiple plates are layered so that the through-holes for each of the multiple plates are partially overlapped. By this configuration, it is possible to supply the liquid, in which fine foreign materials are also eliminated, and to prevent the nozzles from being clogged. Moreover, since the multiple plates are layered, it is possible to suppress the increase of the fabrication costs to form the filter.
However, in the liquid droplet jet apparatus according to Japanese Laid-open Patent Application No. 2008-18662, dispersion of a size of the through-hole to be the filter is caused by micro deviation of layering the multiple plates. Thus, there is a problem in which the foreign materials are not effectively eliminated. Moreover, the plates, in which the multiple through-holes are formed, may be deformed and damaged by a load driving a piezoelectric actuator corresponding to the energy applying unit. Furthermore, the number of parts increase to form the filter by the multiple plates, and it is inevitable to increase the fabrication costs.